A Study of the Protective Properties of a Combined Cermet Material upon a High-Speed Impact

Technical Physics - The ballistic resistance of a combined cermet material based on a high-hardness ceramic bound with an intermetallide on a high-strength metal substrate, (TiB2 + NiTi) + Ti, is...     

Influence of the Degree of Deacetylation of Chitosan and BMP-2 Concentration on Biocompatibility and Osteogenic Properties of BMP-2/PLA Granule-Loaded Chitosan/β-Glycerophosphate Hydrogels

Compositions based on chitosan/β-glycerophosphate hydrogels with highly porous polylactide granules can be used to obtain moldable bone graft materials that have osteoinductive and osteoconductive properties. To eliminate the influence of such characteristics as chain length, degree of purification, and molecular weight on a designed material, the one-stock chitosan sample was reacetylated to degrees of deacetylation (DD%) of 19.5, 39, 49, 55, and 56. A study of the chitosan/β-glycerophosphate hydrogel with chitosan of a reduced DD% showed that a low degree of deacetylation increased the MSCs (multipotent stromal cells) viability rate in vitro and reduced the leukocyte infiltration in subcutaneous implantation to Wistar rats in vivo. The addition of 12 wt% polylactide granules resulted in optimal composite mechanical and moldable properties, and increased the modulus of elasticity of the hydrogel-based material by approximately 100 times. Excessive filling of the material with PLA (polylactide) granules (more than 20%) led to material destruction at a ~10% strain. Osteoinductive and osteoconductive properties of the chitosan hydrogel-based material with reacetylated chitosan (39 DD%) and highly porous polylactide granules impregnated with BMP-2 (bone morphogenetic protein-2) have been demonstrated in models of orthotopic and ectopic bone formation. When implanted into a critical-size calvarial defect in rats, the optimal concentration of BMP-2 was 10 μg/mL: bone tissue areas filled the entire material’s thickness. Implantation of the material with 50 μg/mL BMP-2 was accompanied with excessive growth of bone tissue and material displacement beyond the defect. Significant osteoinductive and osteoconductive properties of the material with 10 μg/mL of BMP-2 were also shown in subcutaneous implantation.     

Reaction of N,N-Dichlorosulfonamides with Ethynyl(trimethyl)silane

Russian Journal of Organic Chemistry - Ethynyl(trimethyl)silane reacted with N,N-dichloroarenesulfonamides to give unstable N-[2,2-di­chloro-2-(trimethylsilyl)ethylidene]arenesulfonamides...     

Synthesis and antiherpetic activity of novel purine conjugates with 7,8-difluoro-3-methyl-3,4-dihydro-2H-1,4-benzoxazine

Chemistry of Heterocyclic Compounds - A method for the synthesis of novel purine conjugates with 7,8-difluoro-3-methyl-3,4-dihydro-2H-1,4-benzoxazine containing fragments of ω-amino acids with...     

Ethylene polymerization and ethylene-1-hexene copolymerization over immobilized metallocene catalysts

Ethylene polymerization and ethylene-1-hexene copolymerization in the presence of metallocene catalysts based on Cp₂ZrCl₂, rac-Et(Ind)₂ZrCl₂, rac-Me₂Si(2-Me-4-Ph-Ind)₂ZrCl₂, and rac-Me₂Si(2-Me-4-Ph-Ind)₂HfCl₂ been investigated. The catalysts have been immobilized on montmorillonite (MMT) containing methylaluminoxanes (MMT-H₂O)/AlMe₃ or isobutylaluminoxanes (MMT-H₂O)/ Ali-Bu₃ synthesized directly on the support surface. The immobilized catalysts, with the general formula (MMT-H₂O)/AlR₃/Zr(Hf)-cene, show a high activity comparable with the activity of the respective homogeneous systems, which depends on the nature of the metal and on the metallocene composition and structure. The catalytic properties of the metallocene systems depend strongly on the nature of the activator as a component of the catalytic complex. (MMT-H₂O)/Ali-Bu₃ is a more effective activator of the hafnocene precatalyst in the polymerization processes than oligomeric methylaluminoxane or methylaluminoxane synthesized on the support. The immobilization of the metallocenes on (MMT-H₂O)/AlR₃ leads to an increase in the molar mass of polyethylene and ethylene-1-hexene copolymers relative to the molar mass of the polymers synthesized using the respective homogeneous systems. The immobilized metallocene catalysts display high selectivity toward the insertion of a higher α-olefin (1-hexene) into the polymer chain, retaining this important property of their homogeneous counterparts.     

Heterogeneous doping of sulfide-conducting phases based on calcium and barium thiolanthanates

The chemical method of preparation of oxide precursors was used to obtain sulfide-conducting ionic salts of CaY₂S₄, BaSm₂S₄ and heterogeneous additives of ZrS₂ and SiS₂, accordingly. The sintering modes for obtaining the heterogeneous systems of CaY₂S₄–ZrS₂ and BaSm2S4–SiS2 were chosen. Samples were characterized using the methods of X-ray phase analysis and microprobe analysis. The methods of thermogravimetric and differential thermal analysis were used to determine thermal stability of samples. The temperature and concentration dependences of conductivity and average ionic transport numbers were studied. The range of compositions of heterogeneous mixtures is determined in which conductivity considerably exceeds conductivity of the basic sulfide-conducting solid electrolytes.     

High-strength biocompatible hydrogels based on poly(acrylamide) and cellulose: Synthesis, mechanical properties and perspectives for use as artificial cartilage

New composite hydrogels based on cellulose and poly(acrylamide) have been synthesized via radical polymerization of acrylamide in cellulose swollen in a reaction solution. In this study, both a plant form of cellulose and a bacterial form—that cultivated by Acetobacter xylinum bacteria—were used. The behavior of synthesized hydrogels during swelling in water, as well as the behavior of the samples swollen at equilibrium during deformation under uniaxial compression under various test conditions, have been studied. A comparative analysis of the main mechanical characteristics of hydrogels and the appropriate data for various types of articular cartilage, one of which—rabbit knee meniscus—has been tested in this study, has been performed. An average-strength hydrogel is very close to articular cartilage in all mechanical characteristics. The degrees of loading at the highest compression deformations observed during the function of joint cartilage (30–50%) is in the range 4–12 MPa for this hydrogel, and the average values of the compression modulus in the deformation ranges of 10–15 and 25–30% are 8.8 and 23.7 MPa, respectively. The behavior of hydrogels and rabbit meniscus under cyclic compression with the amplitude of 50% has been studied. Hydrogels and meniscus under this test conditions demonstrate clear viscoelastic behavior, evidenced by noticeable hysteresis for the first cycle and a decrease in the value of the maximum load with an increase in the number of cycles. Structural features of hydrogels, which can affect the behavior of the hydrogels under study, have been considered. On the whole, the results demonstrate the possibility of modeling the mechanical behavior of cartilage with the use of hydrogels of this type.     

A duality principle in weighted Sobolev spaces on the real line

An embedding inequality of Sobolev type is characterized in the paper with help of a duality principle and boundedness criteria for the Hardy–Steklov integral operator in weighted Lebesgue spaces.